It is known for such cushions or mattresses to be made by juxtaposing cells that are inflatable from a lower orifice that is subsequently closed, and that are fixed in communication with one another on a support that acts as a sole plate and support for the cushion or mattresses as a whole; said cells are elongate in shape, vertical, perpendicular to said supporting soleplate, disposed adjacent to one another, made of a material that is flexible and airtight, and their outside shape is that of a chuck, preferably a four-faced chuck, each face forming a concave indentation or "recess", even when the cell is preinflated and in a rest position, i.e. in a position when the cushion or mattress is not carrying a load.
When a person sits down or lies down on the cushion or mattress, said cells are compressed and their initially recessed side walls deform under such pressure to come into contact with the side walls of adjacent cells, and this continues until the top walls of the cells also come into contact to form an almost continuous surface that supports the surface of the facing portion of the person's body, and fits closely round said shape; since all of the cells are at the same internal pressure, their volume differences compensate mutually.
Such structures are known and they are referred to as being "multicellular" or as being made up of "telescopic" cells. They have been developed by numerous manufacturers and one of the earliest, Mr. Robert H. Graebe, filed a patent application on May 16, 1973 in the United States, which patent was granted on Mar. 11, 1975 under the U.S. Pat. No. 3,870,450. Thereafter various improvement patents based on that basic patent have been filed, for example U.S. Pat. No. 4,541,136 dated Sep. 17, 1985, which relates to the shape of the cells which have four convex external edges and for concave middle edges, between them defining eight flats simultaneously forming four sides that have indented surfaces plus four ridges, the assembly being symmetrical in shape about a central axis. There is U.S. Pat. No. 4,698,864 of Oct. 13, 1987 which relates essentially to the possibility of certain cells having heights that are different from other cells, as a function of the sitting position. There is U.S. Pat. No. 5,052,068 of Oct. 1, 1991 relating to an improvement that is equivalent to the preceding improvement, in which the cells are still symmetrical, having eight flats that form four ridges and four concave edges in the middles of the four faces, however they are of different shapes. Finally, there is PCT patent WO 92/07,492 published on May 14, 1992 that relates to a particular distribution of air or gas for inflating said cells via a manifold capable of distributing said air or gas into some of the cells in such a manner as to permit different pressures, depending on the zones they occupy in the cushion or the mattress.
Mattresses of the kind described in the earlier patents mentioned above have indeed been manufactured, however those patents were initially taken out for the United States only and at least the earliest of them is now in the public domain, even in the United States.
Various standards also exist in some countries for defining minimum characteristics for such cushions or mattresses, for example the standards laid down in France by the Regional Health Directorate [Direction Regionale de la Sante], and these standards specify, in particular, minimum amounts of crushing, for example: a thickness of not less than 2 cm under the body of the subject, and of at least 3 cm under the thighs of a person prone on the mattress; the mattress should be easy to repair rapidly in the event of tearing since any leakage prevents minimum preinflation of the mattress from providing support by means of a minimum degree of inflation that varies as a function of the weight of the person. The material constituting the walls of the cells in such a cushion or mattress should have a thickness lying in the range 600.mu. to 800.mu., and the wall thickness of the base or soleplate thereof should lie in the range 700.mu. to 900.mu., it should have a breaking strength in both directions of more than 15 MPa and its breaking elongation, likewise in both directions, should be greater than 700%. It should contain a pressure of 50 millibars for more than 48 hours and after spending 24 hours supporting a mass of 90 kg distributed over a 35 cm.times.35 cm plank of wood for a cushion of similar size, it should enable the cushion to maintain a thickness of more than 2 cm.
Thus, to satisfy such standards, while nevertheless providing maximum comfort and optimum manufacture so as to achieve a cost price that is as low as possible, in particular in countries where social service organizations that pay for or reimburse such cushions or mattresses have ceiling prices imposed on them, various manufacturers have developed various manufacturing techniques using cells of different shapes and materials of different compositions, and they have also developed various improvements for distinguishing their own cushions from those of their competitors. However, most of them still suffer from certain drawbacks and defects, such as the following for example: instability of the preinflated cells which may topple over when a patient bears against them and/or moves on the cushion or mattress, thereby eliminating the effect and the advantage of having such cells; poor transmission between the volumes of air inside the cells which has the effect, particularly when the person moves, of impeding good distribution of pressure such that pressure is no longer uniform; imperfect adhesion between the various elements; flexibility of the material that is too sensitive to temperature, with the material often being too stiff due to manufacturing techniques that involve soaking; great difficulty or even complete impossibility in repairing leaks; poor external airing and air flow between the cells; . . . .